In the area of superconducting machines and superconducting magnetic coils, there are known coil devices in which superconducting wires or strip conductors are wound in coil windings. For classic low-temperature superconductors such as NbTi and Nb3Sn, usually conductors in the form of wire are used. On the other hand, the high-temperature superconductors, or high-Tc superconductors (HTS), are superconducting materials with a transition temperature above 25 K and, in the case of some classes of material, above 77 K. These HTS conductors typically take the form of flat strip conductors, which have a strip-form substrate strip and a superconducting layer arranged on the substrate strip.
In addition, the strip conductors often also have further layers, such as stabilizing layers, contact layers, buffer layers and in some cases also insulating layers. The most important class of material of the so-called HTS conductors of the second generation (2G-HTS) are compounds of the type REBa2Cu3Ox, where RE stands for an element of the rare earths or a mixture of such elements.
The substrate strip may be formed from steel or of the alloy Hastelloy. The electrical contact with an external circuit is usually established by way of a contact layer of copper, this contact layer either being applied on one side over the superconducting layer or being able to surround the entire strip conductor as an enclosing layer. In both configurations, it is more favorable to establish the contact on the side of the substrate strip that carries the superconducting layer. This side of the strip conductor is referred to hereinafter as the contact side. With contacting on the rear side, that is to say on the side of the substrate facing away from the superconducting layer, higher contact resistances occur, which leads to greater electrical losses and a considerable need for cooling in these regions.
In the case of a superconducting coil winding in which multiple layers of a strip conductor come to lie one on top of the other in multiple turns, it is often difficult to contact both ends of the coil winding on the contact side. With winding techniques that are used as standard for producing disk windings, the contact side of the strip conductor will usually come to lie on the inside either on the inner side or on the outer side of the winding. In order nevertheless to create a low-resistance contact on the contact side of the strip conductor, in the case of known coil devices a specially designed contact piece is used and is inserted into the winding next to the contact side of the strip conductor. However, a complex production process is necessary for such a coil device since special measures have to be taken at the location of this contact piece to ensure the necessary mechanical stability. If a wet winding process with an epoxy adhesive is used, then a packing block, for example of Teflon, must first be inserted in order to keep the location that is to be contacted free from adhesive. After removing the packing block, a soldered connection with a contact piece of copper may be produced for example for the contacting of this location. Since, however, this contact lies within the winding, to produce the necessary mechanical stability the contact region must subsequently be fixed with binding bands of glass-fiber-reinforced plastic and epoxy adhesive.
The German application 102012223366.0, which is not a prior publication, discloses a superconducting coil winding with at least two strip conductors, which respectively have a contact side. Within a coil winding of the coil device, the first and second strip conductors are electrically connected by way of an inner contact between their contact sides. The first and second strip conductors differ in terms of their orientation with respect to the center of the coil, so that this inner contact has the effect that the orientation of the contact side is turned. This makes freely accessible contacting of the contact side possible both on the inner side and on the outer side of the coil winding. The disadvantage of the coil winding disclosed there is, however, that the additional inner contact has the effect of creating a further normally conducting connection within the coil, and therefore the superconducting properties of the coil are interrupted in its interior, and electrical losses occur there together with a greater development of heat.